Implantable medical devices are commonly used today to monitor and/or delivery therapy to a patient, including cardiac simulation therapy. Many patients suffer from heart conditions that can result in a reduced ability of the heart to deliver sufficient amounts of blood to the patient's body. Such heart conditions may lead to slow, rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these conditions, various medical devices (e.g., pacemakers, defibrillators, etc.) are often implanted in a patient's body. Such devices may monitor and in some cases provide electrical stimulation (e.g. pacing, defibrillation, etc.) to the heart to help the heart operate in a more normal, efficient and/or safe manner. To extend the effective lifetime of such implanted devices, there is a desire to conserve energy while still providing effective therapy to the patient.